Dehydrogenation catalyst compositions

ABSTRACT

A novel dehydrogenation process is disclosed. This process comprises contacting dehydrogenatable hydrocarbons with a catalytic composite comprising a platinum component, a tin component, a potassium component, a lithium component, and an alumina support, wherein the lithium to potassium atomic ratio of said catalytic composite is in the range of from 3:1 to 5:1. The process of the invention has particular utility for the dehydrogenation of C 3  -C 30  paraffins.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of prior copendingapplication Serial No. 766,174 filed Aug. 16, 1985, which is a divisionof application Serial No. 676,444 filed Nov. 29, 1984, now U.S. Pat. No.4,595,673.

BACKGROUND OF THE INVENTION

This invention relates to the conversion of hydrocarbons, especially thedehydrogenation of dehydrogenatable hydrocarbons, in the presence of acatalyst composite. This invention also pertains to a new catalystcomposite and a method of making it.

Dehydrogenating hydrocarbons is an important commercial hydrocarbonconversion process because of the great demand for dehydrogenatedhydrocarbons for the manufacture of various chemical products such asdetergents, high octane gasolines, pharmaceutical products, plastics,synthetic rubbers, and other products well known to those skilled in theart. One example of this process is dehydrogenating isobutane to produceisobutylene which can be polymerized to provide tackifying agents foradhesives, viscosity-index additives for motor oils and impact-resistantand anti-oxidant additives for plastics.

INFORMATION DISCLOSURE

It is well known to catalyze the conversion of hydrocarbons with solidcatalysts comprising platinum group metals. For example, U.S. Pat. No.4,072,602 discloses a nonacidic multicomponent catalytic compositecomprised of a platinum group component, a Group IVA component, a GroupVIB transition metal component and an alkali or alkaline earth metalcomponent. The patent limits its teachings to the use of a singlecompound selected from the alkali or alkaline earth metals. For example,the patent states at column 11, lines 20-25 that "best results areobtained when this component is a compound of lithium or potassium." Thepatent thus completely fails to suggest that a dehydrogenation catalystas claimed could advantageously employ a combination of lithium andpotassium. Similarly, U.S. Pat. No. 3,939,220 discloses adehydrogenation catalyst which comprises a platinum or palladiumcomponent, an indium component, a rhenium component, a tin component andan alkali or alkaline earth component. This patent suffers from the samedeficiencies as the '602 patent in that it teaches only the use of asingle alkali or alkaline earth metal component.

U.S. Pat. No. 4,506,032 is similar to the previously discussed patentsin that it is directed to a dehydrogenation catalyst comprised of aplatinum group component, a Group IVA component and an alkali oralkaline earth metal component. Although the patent does teach thatmixtures of one of the alkali or alkaline earth metal group may beemployed, the patent is totally silent with regard to the specificcombination of lithium and potassium in such a catalyst.

U.S. Pat. Nos. 2,479,109 and 2,479,110 disclose a catalyst comprisingplatinum on alumina combined with halogen for reforming, hydrogenating,hydrocracking, oxidizing and dehydrogenating reactions. The term"reforming" in these patents means simultaneously dehydrogenating,isomerizing, cyclizing and cracking a gasoline feedstock. The combinedhalogen component of this catalyst contributes to a controlled type ofcracking activity. The halogen content is preferably maintained belowabout 8 wt. % of the alumina to avoid excessive side reactions,including cracking reactions, which result in excessive gas formationand low liquid volume yield of reformed products. These patents do notdisclose utilizing an alkali component.

U.S. Pat. No. 2,930,763 discloses a two-step process for reforminghydrocarbons. In the first step a hydrocarbon fraction containingunsaturated compounds and/or nitrogen, sulfur or oxygen compounds iscontacted with hydrogen in the presence of a catalyst comprisingplatinum and an alkali metal component on alumina to hydrogenate andsaturate the unsaturated compounds and/or reduce the nitrogen, sulfur oroxygen content of the hydrocarbon fraction. In the second step of thisprocess the treated hydrocarbon fraction from the first step iscontacted at reforming conditions with a conventional reforming catalystcomprising platinum and combined halogen on alumina. Optionally thecatalyst utilized in the first step may contain halogen. A catalystconsisting essentially of alumina, from about 0.01% to about 1% byweight of platinum, from about 0.1% to about 1% by weight of combinedhalogen, and from about 0.01% to about 1% by weight of an alkali metalis recited in Claim 2 of this patent. This patent does not discloseutilizing a Group IVA component.

U.S. Pat. No. 3,531,543 discloses dehydrogenating hydrocarbons with acatalyst comprising platinum, tin and neutralized metal oxide carrier.The preferred carriers are oxide materials whose intrinsic acidity issubstantially neutralized by an alkali or alkaline earth metalcomponent. Pure alumina, for example, has such intrinsic acidity. (cf.Pines and Haag, Journal of the American Chemical Society, 82, 2471(1960)). For example, alumina catalyzes the skeletal isomerization ofolefins, dehydrates alcohols and strongly chemisorbs amines. Also, withincreasing amounts of alkali present, there is a parallel decrease inthese acidic alumina properties. Preferably, the carrier of this patentis a nonacidic lithiated alumina. Preferably, the catalysts of thispatent are prepared from halogen-free compounds. Compounds containinghalogen may be used to manufacture the catalyst provided the halogenresidue is efficiently removed from the final catalyst composite.

U.S. Pat. No. 3,745,112 discloses a catalyst for reforming hydrocarbonswhich comprises a platinum group component, a tin component and ahalogen component with a porous carrier material. This patent disclosesalso that a platinum-tin-alkali or alkaline earth composite is aparticularly effective catalyst for dehydrogenating hydrocarbons. In thedehydrogenation catalyst composite of this patent wherein the alkali oralkaline earth component is added, the amount of halogen, if notentirely eliminated, is minimized in order to minimize or neutralize theacidic functions of the alumina and halogen components which tend topromote hydrocarbon cracking and isomerization side reactions which arenot desired in commercial dehydrogenation processes.

U.S. Pat. No. 3,892,657 discloses that indium is a good promoter forplatinum group-containing catalysts when the atomic ratio of indium toplatinum is from about 0.1:1 to about 1:1. This patent discloses alsothat a Group IVA component selected from the group of germanium, tin,and lead can be added to the acidic form of the indium-containingcatalysts for reforming applications. The acidic form of this catalyst,then, comprises a platinum group component, a Group IVA component, anindium component, a halogen component and a porous carrier material. Theacidic catalyst contains up to about 3.5 wt. % halogen for reformingapplications and up to about 10 wt. % halogen for isomerization andcracking applications. In the dehydrogenation catalyst of this patentwherein the alkali or alkaline earth component is added, however, thehalogen content is maintained at the lowest possible value (about 0.1wt. %).

U.S. Pat. No. 3,909,451 discloses a new method for making adehydrogenation catalyst comprising a platinum component, a tincomponent and an alkali or alkaline earth component. In Example V thispatent discloses a platinum, tin and potassium composition comprisingless than 0.2 wt. % combined chloride.

U.S. Pat. Nos. 4,329,258 and 4,363,721 disclose a catalyst comprising aplatinum group metal, tin, an alkali or alkaline earth metal andcombined halogen element with a refractory oxide-mineral carrier. Theatomic ratio of alkali or alkaline earth metal to platinum group metalfor catalysts of these patents is from 0.2 to 10. The patenteesdiscovered that parts-per-million quantities of alkali or alkaline earthcomponent added to catalyst containing a platinum group metal, tin andhalogen helped increase the C₅ + yield in a reforming process.

British Pat. No. 1,499,297 discloses a dehydrogenation catalystcomprising platinum, at least one of the elements gallium, indium andthallium, and an alkali metal, especially lithium or potassium, withalumina as the carrier material. The catalysts of this patent alsocontain a halogen in an amount of from 0.01 to 0.1 wt. %. The halogencontent is purposely reduced to within this low weight % range in orderto increase the selectivity and stability of the catalyst.

In the prior art dehydrogenation catalysts acknowledged above comprisinga platinum group component, a Group IVA component and an alkali oralkaline earth component wherein the atomic ratio of the alkali oralkaline earth component to the platinum group component is more than10, then, the halogen component has been eliminated completely orotherwise maintained at the lowest possible level, generally less than0.1 wt. %, and always less than 0.2 wt. %, calculated on an elementalbasis.

U.S. Pat. No. 3,996,304, at column 18, beginning at line 47, discloses acatalytic composite comprising an alumina-containing refractoryinorganic oxide, a tin component, a rhodium component, a platinum orpalladium component, and an alkali metal component. The alkali metalcomponent is taught as preferably comprising potassium and/or lithium.The catalyst is taught to have specific utility as a selectivehydrogenation catalyst for the hydrogenation of conjugated diolefinichydrocarbons to monoolefinic hydrocarbons. Although the reference doesdisclose that the alkali metal component may comprise potassium and/orlithium, it does not disclose the specific catalyst of the presentinvention wherein the alkali component comprises from about 0.5 to about2 wt. %, on the weight of the composite of a first alkali metal, andfrom about 0.05 to about 3 wt. %, on the weight of the composite of asecond alkali metal. As will be hereinafter set forth in the examples,the broad teachings relating to the prior art hydrogenation catalystcannot be considered anticipatory of the novel catalytic composite ofthe present invention.

Surprisingly, it has been discovered that by incorporating into thecatalyst a first and a second alkali metal component, there results animproved catalytic composite.

OBJECTS AND EMBODIMENTS

It is, therefore, an object of the present invention to provide animproved process for the conversion of hydrocarbons and especially forthe dehydrogenation of hydrocarbons.

Accordingly in a broad embodiment, the present invention is directed toa process for dehydrogenating dehydrogenatable hydrocarbons comprisingcontacting the dehydrogenatable hydrocarbons at dehydrogenationconditions with a catalytic composite comprising a platinum component, atin component, a potassium component, a lithium component, and analumina support, wherein the lithium to potassium atomic ratio of saidcatalytic composite is in the range of from 3:1 to 5:1.

DETAILED DESCRIPTION OF THE INVENTION

To summarize, the present invention is an improved dehydrogenationprocess utilizing a novel catalyst comprising platinum, tin, potassium,lithium and an alumina support composited in such a manner to provide alithium to potassium atomic ratio ranging from 3:1 to 5:1.

As indicated above, one feature of the catalyst of the invention is aplatinum group component. The platinum group component may be selectedfrom the group consisting of platinum, palladium, iridium, rhodium,osmium, ruthenium or mixtures thereof. Platinum, however, is thepreferred platinum group component. It is believed that substantiallyall of the platinum group component exists within the catalyst in theelemental metallic state.

Preferably, the platinum group component is well dispersed throughoutthe catalyst. The platinum group component generally will comprise about0.01 to 5 wt. %, calculated on an elemental basis, of the finalcatalytic composite. Preferably, the catalyst comprises about 0.1 to 2.0wt. % platinum group component, especially about 0.1 to about 2.0 wt. %platinum component.

The platinum group component may be incorporated in the catalyticcomposite in any suitable manner such as, for example, bycoprecipitation or cogelation, ion exchange or impregnation, ordeposition from a vapor phase or from an atomic source or by likeprocedures either before, while or after other catalytic components areincorporated. The preferred method of incorporating the platinum groupcomponent is to impregnate the carrier material with a solution orsuspension of a decomposable compound of a platinum group metal. Forexample, platinum may be added to the support by commingling the latterwith an aqueous solution of chloroplatinic acid. Another acid, forexample, nitric acid or other optional components may be added to theimpregnating solution to further assist in dispersing or fixing theplatinum group component in the final catalyst composite.

Regarding the Group IVA component, it may be selected from the group ofgermanium, tin, lead or mixtures thereof. Tin, however, is the preferredGroup IVA component. The Group IVA component may be present as acompound such as the oxide, for example, or combined with the carriermaterial or with the other catalytic components. Preferably, the GroupIVA component is well dispersed throughout the catalyst. The Group IVAcomponent generally will comprise about 0.01 to 5 wt. %, calculated onan elemental basis, of the final catalyst composite. Preferably, thecatalyst comprises about 0.2 to about 3.0 wt. % . Group IVA component,especially about 0.2 to about 3.0 wt. % tin.

The Group IVA component may be incorporated in the catalytic compositein any suitable manner such as, for example, by coprecipitation orcogelation, ion exchange or impregnation or by like procedures eitherbefore, while or after other catalytic components are incorporated. Apreferred method of incorporating the tin component is cogelling itduring preparation of the porous carrier material. For example, tin maybe incorporated in an alumina carrier material by mixing a soluble tincompound such as stannous or stannic chloride with an alumina hydrosol,adding a gelling agent such as hexamethylenetetramine and dropping themixture into an oil bath to form spheres containing alumina and tin. Apreferred method of incorporating the germanium component is toimpregnate the carrier material with a solution or suspension of adecomposable compound of germanium such as germanium tetrachloridedissolved in an alcohol. Likewise, the lead component may be impregnatedfrom a solution of lead nitrate in water.

Regarding the alkai metal components, it is essential that the catalyticcomposite contains both a lithium and a potassium component. We believethat the lithium and potassium components exist in the final catalyticcomposite in an oxidation state above that of the elemental metal. Thelithium and potassium components may be present as a compound such asthe oxide, for example, or combined with the carrier material or withthe other catalytic components.

Preferably, the lithium and potassium are well dispersed throughout thecatalytic composite. The lithium component generally will comprise fromabout 0.05 to about 2.0 wt. % of the final catalytic composite, and fromabout 0.05 to about 10.0 wt. % of potassium, calculated on an elementalbasis, of the final catalytic composite. Best results are obtained whenthe catalytic composite has an atomic ratio of lithium to potassiumranging from 3:1 to 5:1 and at least a total of 8.0×10⁻² moles ofpotassium plus lithium per 100 g of said composite. An alternativemeasure of the preferred lithium to potassium concentration is theatomic ratios of lithium to platinum and potassium to platinum. It ispreferred that the atomic ratio of lithium to platinum be at least 25:1and the potassium to platinum ratio be less than 15:1.

The lithium and potassium components may be incorporated in thecatalytic composite in any suitable manner such as, for example, bycoprecipitation or cogelation, by ion exchange or impregnation, or bylike procedures either before, while or after other catalytic componentsare incorporated. A preferred method of incorporating the lithium andpotassium components is to impregnate the carrier material with asolution of potassium chloride and lithium nitrate.

Regarding the porous carrier material, it is preferably a porous,adsorptive support with high surface area of from about 5 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process. It isintended to include within the scope of our invention the use of carriermaterials which have traditionally been utilized in hydrocarbonconversion catalysts such as, for example; (1) activated carbon, coke,or charcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates, including synthetically prepared and naturally occurringones, which may or may not be acid treated, for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, bauxite; (4) refractoryinorganic oxides such as alumina, titanium dioxide, zirconium dioxide,chromium oxide, beryllium oxide, vanadium oxide, cerium oxide, hafniumoxide, zinc oxide, magnesia, boria, thoria, silica-alumina,silicamagnesia, chromia-alumina, alumina-boria, silica-zirconia, etc.;(5) crystalline zeolitic aluminosilicates such as naturally occurring orsynthetically prepared mordenite and/or faujasite, for example, eitherin the hydrogen form or in a form which has been exchanged with metalcations, (6) spinels such as MgAl₂ O₄, FeAl₂ O₄, ZnAl₂ O₄, CaAl₂ O₄, andother like compounds having the formula MO-Al₂ O₄ where M is a metalhaving a valence of 2; and (7) combinations of materials from one ormore of these groups. The preferred carrier material for our catalyst isalumina, especially gamma- or eta-alumina.

The preferred alumina carrier material may be prepared in any suitablemanner from synthetic or naturally occurring raw materials. The carriermay be formed in any desired shape such as spheres, pills, cakes,extrudates, powders, granules, etc., and it may be utilized in anyparticle size. A preferred shape of alumina is the sphere. A preferredparticle size is about 1/16 inch in diameter, though particles as smallas about 1/32 inch, and smaller, may also be utilized.

To make alumina spheres aluminum metal is converted into an alumina solby reacting it with a suitable peptizing acid and water, and thendropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are readilyconverted into the preferred gamma- or eta-alumina carrier material byknown methods including aging, drying and calcining. To make aluminacylinders, an alumina powder is mixed with water and enough of asuitable peptizing agent such as nitric acid, for example, until anextrudable dough is formed. The dough is then extruded through asuitably sized die and cut to form extrudate particles. Other shapes ofthe alumina carrier material may also be prepared by conventionalmethods. After the alumina particles are shaped generally they are driedand calcined. The alumina carrier may be subjected to intermediatetreatments during its preparation, including washing with water or asolution of ammonium hydroxide, for example, which treatments are wellknown in the art.

The catalytic composite of our invention may also contain a halogencomponent. The halogen component may be either fluorine, chlorine,bromine or iodine or mixtures thereof. Chlorine and bromine are thepreferred halogen components. The halogen component is generallypresent, we believe, in a combined state with the porous carriermaterial and alkali component. Preferably, the halogen component is welldispersed throughout the catalytic composite. The halogen component maycomprise from more than 0.1 wt. % to about 15 wt. %, calculated on anelemental basis, of the final catalytic composite.

The halogen component may be incorporated in the catalytic composite inany suitable manner, either during the preparation of the carriermaterial or before, while or after other catalytic components areincorporated. For example, the alumina sol utilized to form thepreferred aluminum carrier material may contain halogen and thuscontribute at least some portion of the halogen content in the finalcatalyst composite. Also, the halogen component or a portion thereof maybe added to the catalyst composite during the incorporation of thecarrier material with other catalyst components, for example, by usingchloroplatinic acid to impregnate the platinum component. Also, thehalogen component or a portion thereof may be added to the catalystcomposite by contacting the catalyst with the halogen or a compound,solution, suspension or dispersion containing the halogen before orafter other catalyst components are incorporated with the carriermaterial. Suitable compounds containing the halogen include acidscontaining the halogen, for example, hydrochloric acid. Or, the halogencomponent or a portion thereof may be incorporated by contacting thecatalyst with a compound, solution, suspension or dispersion containingthe halogen in a subsequent catalyst regeneration step. In theregeneration step carbon deposited on the catalyst as coke during use ofthe catalyst in a hydrocarbon conversion process is burned off thecatalyst and the platinum group component on the catalyst isredistributed to provide a regenerated catalyst with performancecharacteristics much like the fresh catalyst. The halogen component maybe added during the carbon burn step or during the platinum groupcomponent redistribution step, for example, by contacting the catalystwith a hydrogen chloride gas. Also, the halogen component may be addedto the catalyst composite by adding the halogen or a compound, solution,suspension or dispersion containing the halogen, such as propylenedichloride, for example, to the hydrocarbon feed stream or to therecycle gas during operation of the hydrocarbon conversion process.

Optionally, the catalyst of our invention may also contain a sulfurcomponent. Generally, the sulfur component may comprise about 0.01 to 2wt. %, calculated on an elemental basis, of the final catalyticcomposite. The sulfur component may be incorporated into the catalyticcomposite in any suitable manner. Preferably, sulfur or a compoundcontaining sulfur such as hydrogen sulfide or a lower molecular weightmercaptan, for example, is contacted with the catalyst composite in thepresence of hydrogen at a hydrogen to sulfur ratio of about 100 and atemperature of from about 10° to about 540° C., preferably underwater-free conditions, to incorporate the sulfur component.

Optionally, the catalyst may also contain other, additional componentsor mixtures thereof which act alone or in concert as catalyst modifiersto improve catalyst activity, selectivity or stability. Some well-knowncatalyst modifiers include antimony, arsenic, bismuth, cadmium,chromium, cobalt, copper, gallium, gold, indium, iron, manganese,nickel, rhenium, scandium, silver, tantalum, thallium, titanium,tungsten, uranium, zinc, and zirconium. These additional components maybe added in any suitable manner to the carrier material during or afterits preparation, or they may be added in any suitable manner to thecatalytic composite either before, while or after other catalyticcomponents are incorporated. It is preferred that these additionalcomponents are present in the catalyst formulation in an amount from0.05 to 5 wt. %.

Preferably, the catalyst of our invention is nonacidic. "Nonacidic" inthis context means that the catalyst has very little skeletalisomerization activity, that is, the catalyst converts less than 10 mole% of butene-1 to isobutylene when tested at dehydrogenation conditionsand, preferably, converts less than 1 mole %. The acidity of thecatalyst can be decreased if necessary to make the catalyst nonacidic byincreasing the amount of the alkali component within the claimed range,or by treating the catalyst with steam to remove some of the halogencomponent.

After the catalyst components have been combined with the porous carriermaterial, the resulting catalyst composite will generally be dried at atemperature of from about 100° to about 320° C. for a period oftypically about 1 to 24 hours or more and thereafter calcined at atemperature of about 320° to about 600° C. for a period of about 0.5 toabout 10 or more hours. Finally, the calcined catalyst composite istypically subjected to a reduction step before use in the hydrocarbonconversion process. This reduction step is effected at a temperature ofabout 230° to about 650° C. for a period of about 0.5 to about 10 ormore hours in a reducing environment, preferably dry hydrogen, thetemperature and time being selected to be sufficient to reducesubstantially all of the platinum group component to the elementalmetallic state.

The instant invention utilizes the catalytic composite describedhereinabove in a process where dehydrogenatable hydrocarbons arecontacted with the catalytic composite in a dehydrogenation zonemaintained at dehydrogenation conditions. This contacting may beaccomplished in a fixed catalyst bed system, a moving catalyst bedsystem, a fluidized bed system, etc., or in a batch-type operation. Afixed bed system is preferred. In this fixed bed system the hydrocarbonfeed stream is preheated to the desired reaction temperature and thenpassed into the dehydrogenation zone containing a fixed bed of thecatalyst. The dehydrogenation zone may itself comprise one or moreseparate reaction zones with heating means therebetween to ensure thatthe desired reaction temperature can be maintained at the entrance toeach reaction zone. The hydrocarbon may be contacted with the catalystbed in either upward, downward or radial flow fashion. Radial flow ofthe hydrocarbon through the catalyst bed is preferred for commercialscale reactors. The hydrocarbon may be in the liquid phase, a mixedvapor-liquid phase or the vapor phase when it contacts the catalyst.Preferably, it is in the vapor phase.

Hydrocarbons which may be dehydrogenated include dehydrogenatablehydrocarbons having from 2 to 30 or more carbon atoms includingparaffins, alKylaromatics, naphthenes and olefins. One group ofhydrocarbons which can be dehydrogenated with the catalyst is the groupof normal paraffins having from 2 to 30 or more carbon atoms. Thecatalyst is particularly useful for dehydrogenating paraffins havingfrom 2 to 25 or more carbon atoms to the corresponding monoolefins orfor dehydrogenating monoolefins having from 3 to 15 or more carbon atomsto the corresponding diolefins.

Dehydrogenation conditions include a temperature of from about 400° toabout 900° C., a pressure of from about 0.01 to 10 atmospheres and aliquid hourly space velocity (LHSV) of from about 0.1 to 100 hr⁻¹.Generally for normal paraffins the lower the molecular weight the higherthe temperature required for comparable conversion. The pressure in thedehydrogenation zone is maintained as low as practicable, consistentwith equipment limitations, to maximize the chemical equilibriumadvantages.

The effluent stream from the dehydrogenation zone generally will containunconverted dehydrogenatable hydrocarbons, hydrogen and the products ofdehydrogenation reactions. This effluent stream is typically cooled andpassed to a hydrogen separation zone to separate a hydrogen-rich vaporphase from a hydrocarbon-rich liquid phase. Generally, thehydrocarbon-rich liquid phase is further separated by means of either asuitable selective adsorbent, a selective solvent, a selective reactionor reactions or by means of a suitable fractionation scheme. Unconverteddehydrogenation hydrocarbons are recovered and may be recycled to thedehydrogenation zone. Products of the dehydrogenation reactions arerecovered as final products or as intermediate products in thepreparation of other compounds.

The dehydrogenatable hydrocarbons may be admixed with a diluent materialbefore, while or after being passed to the dehydrogenation zone. Thediluent material may be hydrogen, steam, methane, ethane, carbondioxide, nitrogen, argon and the like. Hydrogen is the preferreddiluent. Ordinarily, when hydrogen is utilized as the diluent it isutilized in amounts sufficient to ensure a hydrogen to hydrocarbon moleratio of about 0.1:1 to about 40:1, with best results being obtainedwhen the mole ratio range is about 1:1 to about 10:1. The diluenthydrogen stream passed to the dehydrogenation zone will typically berecycled hydrogen separated from the effluent from the dehydrogenationzone in the hydrogen separation zone.

Water or a material which decomposes at dehydrogenation conditions toform water such as an alcohol, aldehyde, ether or ketone, for example,may be added to the dehydrogenation zone, either continuously orintermittently, in an amount to provide, calculated on the basis ofequivalent water, about 1 to about 20,000 weight ppm of the hydrocarbonfeed stream. About 1 to about 10,000 weight ppm of water addition givesbest results when dehydrogenating paraffins having from 6 to 30 or morecarbon atoms.

To be commercially successful a dehydrogenation catalyst should exhibitthree characteristics, namely high activity, high selectivity and goodstability. Activity is a measure of the catalyst's ability to convertreactants into products at a specific set of reaction conditions, thatis, at a specified temperature, pressure, contact time and concentrationof diluent such as hydrogen, if any. For dehydrogenation catalystactivity, we measured the conversion or disappearance of paraffins inpercent relative to the amount of paraffins in the feedstock.Selectivity is a measure of the catalyst's ability to convert reactantsinto the desired product or products relative to the amount of reactantsconverted. For catalyst selectivity we measured the amount of normalparaffins converted. Stability is a measure of the rate of change withtime on stream of the activity and selectivity parameters--the smallerrates implying the more stable catalysts.

Since dehydrogenation of hydrocarbons is an endothermic reaction andconversion levels are limited by chemical equilibrium, it is desirablein order to achieve high conversion to operate at high temperatures andlow hydrogen partial pressures. At such severe conditions it isdifficult to maintain high activity and selectivity for long periods oftime because undesirable side reactions such as aromatization, cracking,isomerization and coke formation increase. Therefore, it is advantageousto have a new hydrocarbon dehydrogenation catalyst with improvedactivity, selectivity and stability characteristics.

The following examples are introduced to further describe the catalystand process of the invention. The examples are intended as illustrativeembodiments and should not be considered to restrict the otherwise broadinterpretation of the invention as set forth in the claims appendedhereto.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 are graphical representations of the performance in theparaffin dehydrogenation process of Catalyst A, in accordance with theinvention, and Catalyst B, different from the invention.

FIG. 1 is a graph of the normal paraffin conversions in weight percentversus hours on stream of the test.

FIG. 2 is a plot of the selectivities of the catalysts in weight percentfor producing linear olefins versus the linear paraffin conversion inweight percent.

FIGS. 3 and 4 are a graphical depiction of the performance of twofurther catalysts in the paraffin dehydrogenation process. Depicted inthese figures are Catalyst C, different from the invention, and CatalystD, in accordance with the invention.

FIG. 3 is a graphical representation of the conversions of normalparaffins in weight percent versus the hours on stream of tests.

FIG. 4 is a plot of the selectivities of the catalysts for theproduction of normal olefins represented in weight percent versus theconversion of normal paraffins in weight percent.

EXAMPLE I

30.2 g of an alumina support containing tin was impregnated with 4.6 gof a 2.54 wt. % chloroplatinic acid solution, 16.43 g of a 0.8 wt. %lithium nitrate solution, both solutions being further admixed with 1.44g of a 71 wt. % nitric acid solution in 59.6 g of water. The catalystwas then steam-dried for 2 hours and 20 minutes and then subjected tooven drying at about 150° C. for 2 hours. The catalyst was thensubjected to a heating step in air for about 2.5 hours at a temperatureof about 540° C. 29.6 g of the thusly prepared composite was thenfurther subjected to impregnation with a solution comprising about 6.7 gof a 3.4 wt. % potassium chloride solution in about 88.6 g of water. Thecomposite was then steam-dried for 2 hours, oven-dried at 150° C. forabout 2 hours and calcined at about 540 ° C. for 21/2 hours. Thereafterthe catalyst was reduced. The resulting catalyst, designated Catalyst A,comprised about 0.39 wt. % platinum, 0.5 wt. % tin, 0.77 wt. %potassium, 0.44 wt. % lithium, and about 0.75 wt. % chloride. Using 100g of the catalyst as a basis, Catalyst A comprised a total of 8.3×10⁻²moles of lithium plus potassium in a lithium to potassium mole ratio of3.2.

EXAMPLE II

In this example a second catalyst was prepared comprising only a singlealkali metal component. This catalyst was made substantially inaccordance with the procedures employed in Example I above. However, thepotassium impregnation step and subsequent steamdrying, oven-drying andcalcination steps were omitted. Accordingly, the alkali metal componentof this catalyst comprised only lithium. The catalyst of this examplewas designated Catalyst B and comprised about 0.38 wt. % platinum, 0.5wt. % tin, 0.6 wt. % lithium, and 0.1 wt. % chloride. It should be notedthat although Catalyst B contains a different weight percent alkalimetal component than Catalyst A, they both contain approximately thesame total moles of the alkali metal component. Catalysts A and Bcontain about 8.3×10⁻² moles and 8.6×10⁻² moles, respectively, of alkalimetal.

EXAMPLE III

A third catalyst was prepared substantially in accordance with theprocedure set forth above in Example II. Accordingly, this catalyst wasnot made in accordance with the invention and comprised only a singlealkali metal component. The catalyst of this example was designatedCatalyst C and comprised about 0.37 wt. % platinum, about 0.5 wt. % tin,about 0.6 wt. % lithium and about 0.1 wt. % chloride.

EXAMPLE IV

In this example a fourth catalyst was prepared substantially inaccordance with the procedure set forth in Example I. However, in thisinstance a solution of potassium nitrate was substituted for thepotassium chloride. This fourth catalyst, designated Catalyst D,comprised about 0.38 wt. % platinum, about 0.5 wt. % tin, about 0.76 wt.% potassium, about 0.45 wt. % lithium, and about 0.19 wt. % chlorine.Using 100 g of the catalyst as a basis, Catalyst D comprised a total of8.4×10⁻² moles of lithium plus potassium in a lithium to potassium moleratio of 3.3. Therefore, this catalyst was in accordance with theinvention.

EXAMPLE V

In this example Catalysts A and B were evaluated as catalysts for thedehydrogenation of normal paraffins. These evaluated tests were carriedout in a pilot plant comprising a reactor and product separationfacilities. The charge stock was passed into the reaction zone whereinit was contacted with 5 cc of catalyst. The effluent from the reactionzone was thereafter separated and analyzed. The charge stock comprised amixture of C₁₀ -C₁₃ normal paraffins. The reaction zone was maintainedat a pressure of about 20 psig. The charge stock was passed to thereaction zone at a rate sufficient to produce a liquid hourly spacevelocity of about 70 hr⁻¹. Hydrogen diluent was fed to the reaction zoneat a rate sufficient to provide a molar hydrogen to hydrocarbon ratio ofabout 4:1. The feedstock was heated to a temperature of about 495° C.prior to contact with the catalyst. The results of these tests are setforth in FIGS. 1 and 2. FIG. 1 is a plot of the normal paraffinconversion in weight percent versus the number of hours on stream. Thenormal paraffin conversion is defined as the weight of the components inthe fresh feed which actually underwent some reaction divided by thetotal weight of the feed. In FIG. 1 it could be seen that after 20 hoursCatalyst A of the invention exhibited higher conversions than CatalystB. FIG. 2 is a plot of total normal olefin selectivity in weight percentversus the normal paraffin conversion in weight percent. The totalnormal olefin selectivity in weight percent is defined as the weight ofcharge stock components converted to the desired normal olefin productdivided by the total number of charge stock components undergoing somereaction. A review of FIG. 2 discloses that Catalyst A of the inventionshowed higher or comparable selectivity for the production of desirablenormal olefins than did Catalyst B. In summary then, it can be seen thatCatalyst A exhibited higher conversions than Catalyst B over the last 60of the 80 hours of evaluation with higher selectivity for the productionof the desirable normal olefins. It must be remembered that bothcatalysts contained substantially the same total moles of alkali metal.Thus, these results illustrate that the superior performance exhibitedby Catalyst A is due to the unique combination of lithium and potassiumand that such performance is not obtained by merely increasing the totalmoles of a single alkali metal species as was done in preparing CatalystB.

EXAMPLE VI

In the previous example it should be noted that Catalyst A comprisedabout 0.75 wt. % chloride while Catalyst B only contained 0.1 wt. %chloride. In order to substantiate that the improved performance of thecatalyst of the present invention did not result from the higher halogencontent of Catalyst A two further catalysts, Catalysts C and D, weretested. As will be noted in Examples III and IV, Catalysts C and Dcontained about 0.1 and about 0.19 wt. % chloride, respectively.Accordingly, these catalysts contain substantially the same content ofhalogen.

The test procedure employed in the present invention was essentiallythat set forth in Example V above. However, in this case the feedstockto the process comprised C₁₁ -C₁₃ normal paraffins. Additionally, thereaction zone contained a catalyst loading of 10 cc and the liquidhourly space velocity was 40 hr⁻¹. Moreover, the catalyst was subjectedto a presulfiding step having the following procedure. The catalyst wasreduced in the reaction zone in flowing hydrogen at a temperature of495° C. for 5 hours. Thereafter H₂ S was added to the flowing hydrogenin sufficient amount to provide a mixture of 99% hydrogen and 1% H₂ S.This mixture was passed over the catalyst for a further period of fivehours at a temperature of 495° C. After the 5 hour period thehydrogen/H₂ S mixture was cut and feed hydrocarbon and hydrogen diluentwere cut in. The test conditions were then instituted.

The results of testing the catalysts are set forth in FIGS. 3 and 4.FIG. 3 is a graphical representation of the conversions of normalparaffins in weight percent versus the number of hours on stream of theevaluation test. A review of FIG. 3 discloses that Catalyst D, inaccordance with the invention, exhibits higher conversions than doesCatalyst C, a catalyst different than the invention, for the last 70hours of the 80 hour test results depicted. FIG. 4 is a graphical plotof the selectivities of the catalysts for the production of total normalolefins in weight percent versus the normal paraffin conversion inweight percent. A review of FIG. 4 discloses that Catalyst D, inaccordance with the invention, results in improved selectivity for theproduction of desirable normal olefins.

It can, therefore, be seen that the improved results of the catalyst ofthe present invention which were disclosed in Example V were not due tothe halogen content difference between Catalysts A and B. As disclosedin FIGS. 3 and 4, Catalyst D, in accordance with the invention, showedsuperior conversion and selectivity properties to Catalyst C even thoughboth had comparable halogen content.

EXAMPLE VII

To demonstrate both the importance of the combination of lithium andpotassium and the criticality of the atomic ratio of lithium topotassium, three new catalysts were prepared (E, F, and G). Thesecatalysts as well as Catalyst D of Example IV were evaluated in a pilotplant dehydrogenation process. Each of the new catalysts was preparedsubstantially in accordance with the procedure set forth in Example I.However, for these catalysts of this example, a solution of potassiumnitrate was substituted for the potassium chloride.

Table 1 summarizes the properties of the finished catalytic composites.As evident from the data presented, Catalyst D was made in accordancewith the instant invention and Catalysts E, F and G were not.

Each of the catalysts were evaluated as catalysts for thedehydrogenation of normal paraffins following substantially the sametesting procedure as outlined in Example VI. However, in testingCatalysts E, D, F and G, the feedstock (C₁₀ -C₁₃ n-paraffins) was fed tothe reaction zone at a rate sufficient to produce a liquid hourly spacevelocity of 20 hr⁻¹. Conversion of feedstock and selectivity to normalolefins was calculated as set forth in Example V.

A review of the test results presented in Table 1 clearly shows thatCatalyst D of the instant invention performs superior to the othercatalysts not of the invention. It is to be noted that the improvedperformance appears to be directly related to the molar ratio of lithiumto potassium. To further substantiate this effect, another catalyst wasprepared at a higher Li:K molar ratio than Catalyst D.

Catalyst H, not in accordance with the invention, was prepared andevaluated in substantially the same manner as Catalysts E through G,however, the feedstock used during testing comprised of C₁₁ -C₁₃n-paraffins. To allow for a proper comparison to Catalyst H, Catalyst Dwas retested using the same feedstock. Catalyst properties and testresults are shown in Table 2. It is evident from the results that thelithium to potassium ratio is critical to achieving good paraffindehydrogenation performance.

                                      TABLE 1    __________________________________________________________________________                     Molar                         Moles of                     Ratio                         Li + K/100 g                                n-Paraffin Conversion, wt. %    Catalyst.sup.1         Pt Li K  Cl Li/K                         catalyst                                at 30 hrs.                                       at 100 hrs.    __________________________________________________________________________    E    0.427            0.57               0  0.10   0.082  16.1   12.5    D    0.385            0.45               0.76                  0.19                     3.34                         0.084  18.1   15.9    F    0.375            0.40               1.0                  0.17                     2.25                         0.083  10.5   9.7    G    0.370            0.30               1.4                  0.19                     1.20                         0.079  10.5   9    __________________________________________________________________________     .sup.1 Catalysts E-H contained about 0.5 wt. % Sn. Additionally Pt/Li/K/C     are all in wt. %.

                                      TABLE 2    __________________________________________________________________________                     Molar                         Moles of                     Ratio                         Li + K/100 g                                n-Paraffin Conversion, wt. %    Catalyst.sup.1         Pt Li K  Cl Li/K                         catalyst                                at 30 hrs.                                       at 100 hrs.    __________________________________________________________________________    H    0.383            0.47               0.45                  0.12                     5.89                         0.079  12.5    8.2    D    0.385            0.45               0.76                  0.19                     3.34                         0.084  18.4   11.0    __________________________________________________________________________     .sup.1 Catalysts E-H contained about 0.5 wt. % Sn. Additionally Pt/Li/K/C     are all in wt. %.

What is claimed is:
 1. A process for dehydrogenating dehydrogenatablehydrocarbons comprising contacting the dehydrogenatable hydrocarbons atdehydrogenation conditions with a catalytic composite comprising aplatinum component, a tin component, a potassium component, a lithiumcomponent, and an alumina support, wherein the lithium to potassiumatomic ratio of said catalytic composite is in the range of from 3:1 to5:1.
 2. The process of claim 1 further characterized in that thecatalytic composite contains at least a total of 8.0×10⁻² moles ofpotassium plus lithium per 100 g of said composite.
 3. The process ofclaim 1 further characterized in that the lithium to platinum atomicratio is at least
 25. 4. The process of claim 1 further characterized inthat the catalytic composite comprises 0.01 to 2.0 wt. % platinum. 5.The process of claim 1 further characterized in that the catalyticcomposite comprises 0.1 to 15 wt. % of a halogen content.
 6. The processof claim 1 further characterized in that the catalytic compositecomprises 0.05 to 5 wt. % of an indium component.
 7. The process ofclaim 1 further characterized in that the catalytic composite comprises0.05 to 5 wt. % of a gallium component.
 8. The process of claim 1further characterized in that the catalytic composite comprises 0.05 to5 wt. % of a thallium component.
 9. A process for dehydrogenating C₂ toC₃₀ hydrocarbons comprising contacting said hydrocarbons at atemperature from 400° C. to 900° C., a pressure from 0.01 to 10 atm, anda liquid hourly space velocity of from 0.1 to 100 hr⁻¹, with a catalyticcomposite comprising 0.01 to 2.0 wt. % platinum, 0.2 to 3.0 wt. % tin, apotassium component, a lithium component and an alumina support, whereinthe lithium-to-potassium atomic ratio of said catalyst composite is inthe range of from 3:1 to 5:1.